Generally, drop cables are also referred to as DV cables. In many cases, as exemplified in FIG. 7, a drop cable c is strung between a utility pole a and a house b. Generally, in the wiring work for such an aerial drop cable c, a first end of the drop cable c is supported by a supporting tool (not shown) at a mounting point d of the house b. Then a second end side of the drop cable c is pulled up to a mounting point e of the utility pole a, and the drop cable c is tensioned, supported on a supporting tool (not shown), and thereby strung. The wiring length of the aerial drop cable c is generally about 10 m to about 50 m and about 20 m in average. The sag α of the cable strung overhead is defined according to the electricity distribution regulations of an electric power company. More specifically, the size of the electric wire is different (e.g., 3.2 mm2 or less or 14 mm2 or more) depending on the regulations, and the sag is about 2 to 4% of the length of the wire strung overhead, although it varies from season to season. To string the drop cable c with the above sag α maintained, a large tension must be applied to the drop cable c.
As described above, a large tension is transmitted to the drop cable c to pull up the second end side thereof to the mounting point e of the utility pole a and to tension the drop cable c. Since the drop cable c is a low-voltage cable (e.g., for 100 V), it is formed by lightly twisting 2 to 3 wires together to obtain the above size and has a relatively small diameter and low resistance to external force. Therefore, in one method used to transmit the tension, one end of a so-called fiber rope f formed of fibers is wound around the drop cable, as shown in FIG. 5, without using a cable gripping tool (sometimes referred to as “KAMURA”) that clamps the wire between metal members.
To transmit the required tension to the drop cable c through the rope f wound thereon, a first end of the rope f is tightly bound to the drop cable c using a metal binding wire g, and the rope f extending from the tightly bound position toward the tension side is wrapped around the drop cable c at at least 3 positions spaced apart from each other as shown in FIG. 5. In this case, the rope f is wrapped in a simple manner at the intermediate position. However, at the starting position h on the tension side, the rope f is wrapped in a particularly complex manner to prevent slippage. At the end point i to which the tension is not applied, the rope f is wrapped in a relatively complex manner to prevent slippage to some extent. In this manner, the tension directly or indirectly applied to the rope f is transmitted to the drop cable c. At the initial stage of tension transmission, the wrapped portion of the rope f wrapped around the drop cable c is tightened around the drop cable c by the tension and fastens the drop cable c, and therefore the tension is reliably transmitted without slippage.
The tension is directly transmitted to the rope f by pulling down the rope f connected to the drop cable c at a connection portion j shown in FIG. 7. More specifically, a second end of the rope f hung down through a pulley h supported near the mounting point e of the utility pole a is pulled down by, for example, man power, as shown by a phantom line in FIG. 7. Instead of man power, a winding machine or a manual operation wire tensioning device (sometimes referred to as “SHIMERA”) may be used. A connection tool such as a connection ring and a hook may be provided at the second end of the rope f. In this case, the connection tool is connected to a towing source to pull up and tension the second end of the drop cable c.
In any case, the rope f is wrapped around the drop cable c on the ground with the second end side of the drop cable c not pulled up as shown by the phantom line.
However, the second end side may be first pulled up toward the utility pole a and tensioned to some extent, and the drop cable c in a preliminary strung state may then be tensioned so as to satisfy a predetermined sag α. In this procedure, the rope f used for the tensioning operation is wrapped around the drop cable c held in the preliminary strung state, as shown in FIG. 6. In this case, the rope f is wrapped around the drop cable c at a high place as shown in FIG. 6.
In one known method for stringing and laying a cable using a messenger wire, first and second towropes tied together at their ends are used (see, for example, Patent Document 1). A brief description is given of this method. First, the first and second towropes are threaded through pulleys of first and last utility poles corresponding to the leading and trailing ends of the towropes and through pulleys of intermediate utility poles, and the leading and trailing ends of the second towrope are tied to the corresponding first and last utility poles. Next, the leading end of the first towrope is connected to the messenger wire through a swivel, and the trailing end of the first towrope is attached to a captor-in-drum. Then the first towrope is pulled toward the trailing end to string and lay the messenger wire. Next, a cable is connected to the leading end of the second towrope through a swivel. The second towrope is attached to the captor-in-drum and pulled, and the cable is thereby threaded through the pulleys. After the cable is strung, it is detached from the pulleys by a worker on a bucket car and attached to the messenger wire using cable hangers. Finally, the cable is hung from the messenger wire through the cable hangers.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-17011.